From what I've seen Boxers have higher energy, but even with a higher energy GSD I think you'd be able to focus it's energy better. You sound like the perfect owner for a GSD since you enjoy having your dog with you as much as you can. GSDs are so loyal, they will love to be you too!
My foster grandparents had two boxers. They were great, but not as, hmm, people oriented I guess? They were loving dogs, but pretty demanding and high energy. They were beautiful but to me anyway GSD is much easier.